The present invention is concerned with a method for adhesively bonding two surfaces together with a liquid adhesive and particularly is concerned with significantly reducing, if not entirely eliminating, air entrapment in the bond. In addition, the present invention is directed to an assembly for bonding two surfaces together as well as directed to the bonded surfaces obtained according to the present invention. The present invention is especially applicable for binding flat or at least substantially planar surfaces such as used for fabricating microelectronic components such as liquid crystal display assemblies and heat-sink attachments as well as various commercial applications such as windowpane glass and auto windshield applications.
A variety of industrial and commercial applications require bonding surfaces together and, in certain instances, flat surfaces having relatively large areas. Included in these applications are microelectronics applications for bonding liquid crystal display assemblies and especially relatively large liquid crystal display assemblies and heat-sink attachments, and such commercial applications as windowpane glass and auto windshield applications. When laminating or bonding flat surfaces with a liquid adhesive, the ever present problem of air entrapment requires special attention. For instance, even though a surface may appear flat or planar, small topographic variations allow contacting at multiple points during mating. As the adhesive spreads from such multiple points, the advancing fronts can meet and thereby trap pockets of air.
The larger the area of the mating surface, the higher the incidence of air entrapment. Furthermore, the lower the viscosity of the adhesive, the higher the incidence of air entrapment.
Trapped air, depending upon the desired product, presents problems of varying degrees. For instance, when dealing with bonding large liquid crystal display assemblies, the individual LCD tiles are arranged in a matrix and secured to a tile carrier. The tile carrier typically includes a cover plate and a back plate with the LCD tiles sandwiched between them. The bonding of the back plate and cover plate to the liquid crystal display tiles should be as void free as possible. In order to achieve a void free bond, proper dispensing of the adhesive mass along with providing a pattern that allows spreading out from the center outward and sweeping air out as the front advances must be achieved. In addition, the surfaces to be bonded must be mated parallel to each other. It is also desirable that the point contact of the mating surfaces with the adhesive between them be controlled and that the pattern employed permit complete coverage of the surface area of the mating substrates regardless of shape such as rectangular, square or polygon. Also, it is necessary to control the bond line.
With respect to these requirements, the proper dispensing of the adhesive mass can be readily achieved employing metered dispense units well known in the art. Moreover, it has previously been determined that an X pattern extending the entire diagonal length of the surfaces to be bonded is necessary for achieving complete coverage. Furthermore, a majority of the adhesive should be dispensed in the center of the adhesive pattern since spreading is initiated in the center, and spreads out radially. Nevertheless, it has been found that regardless of the pattern geometry in the center, e.g. circular, elliptical, square, smaller scale X pattern and the like, the geometry of the spreading area quickly reverts to circular or elliptical. However, even when employing an X pattern with the diagonal spokes extending all the way to the corners of the surface to be bonded, a void free bond line is not necessarily achieved.
The present invention is concerned with substantially eliminating, if not entirely eliminating, voids when bonding surfaces together and especially flat surfaces. In particular, the present invention is concerned with a method for bonding two flat planar surfaces together. The method of the present invention comprises providing on a major surface of one of the surfaces to be bonded a central single point adhesive contact deposit within the vicinity of the center of the surface. Also provided on a major surface of one of the surfaces is adhesive arranged and extending from a central portion deposit in a spoke-like array diagonally across substantially the entire surface. The two surfaces are mated parallel to each other with the adhesive located between the two surfaces and pressed together to thereby cause the adhesive to spread and cover the surfaces and thereby bond the surfaces together.
The present invention is also concerned with an assembly for bonding two surfaces together which comprises central single point adhesive contact deposit present within the vicinity of the center of one of the surfaces. Also provided on a major surface of one of the surfaces is adhesive arranged and extending from a central portion deposit in a spoke-like array diagonally across substantially the entire surface.
Furthermore, the present invention is concerned with an article that comprises two surfaces bonded together wherein one of the surfaces has a smaller surface area than that of the other of the surfaces. The surfaces are bonded together by an adhesive located between the surfaces and covering the entire area of the smaller surface area and being void free and exhibiting a wavelike undulating fillet profile on the outer perimeter of the smaller surface.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.